As is generally known, butterfly valves, gate valves, ball valves and globe valves have universally been used for regulating and stopping fluid flow.
In most prior art valves, a valve element fixed to a valve element operating shaft is opened and shut by operating a handle or the like. Such valves are economical in their own way as long as the valves are used under moderate service conditions. However, various technical problems arise in the prior art valves due to structural restrictions thereon when the valves are used under severe service conditions for handling high-temperature, high-pressure slurry, corrosive fluids or the like.
Examples of technical problems that may arise in prior art valves will be explained.
(A) As regards butterfly valves, head loss across a butterfly valve due to resistance exerted by the butterfly valve on fluid flow is low when the butterfly valve is in a fully open state. The structure of butterfly valves requires the valve element to sidle up to the valve seat to rest on the valve seat. (Such a mode of closing movement of the valve element will be referred to as "slide sidling mode" for the sake of convenience in the following description.) Movement of the valve element in the slide sidling mode entails the abrasion of sealing surfaces that deteriorates the sealing effect of the sealing surfaces. As is obvious from FIG. 8 showing a prior art butterfly valve, it is difficult to achieve uniform, close contact between the sealing surfaces even if the sealing surfaces are formed in spherical surfaces or an eccentric valve element operating shaft is employed. Furthermore, the valve element and the valve seat will be damaged if a foreign matter is stuck between the sealing surfaces when seating the valve element on the valve seat. Although various attempts, such as putting elastic members on the sealing surfaces, have been made to secure satisfactory sealing contact, those attempts are symptomatic means merely capable of supplementing imperfect sealing contact. Durability of elastic member formed of rubber is insufficient when used under severe service conditions, such as conditions requiring handling high-temperature, high-pressure slurry, corrosive fluids or the like. Elastic members of a metal must be formed in a very intricate construction to provide the elastic members with satisfactory elasticity. If a valve element operating shaft 7 is biased relative to the valve element 4 as shown in FIG. 8, torque necessary for operating the valve element 4 increases and, additional problems in strengthening the valve element operating shaft and increasing valve element driving force arise.
(B) As regards gate valves, the valve element slides substantially in parallel to the valve seat for opening and shutting. Therefore, gate valves exert high resistance on fluid flow, cause rapid abrasion, and need elastic members to be put on the sealing surfaces to secure satisfactory sealing contact, which entails problems similar to those entailed by the butterfly valves.
(C) As regards ball valves, head loss across a ball valve due to resistance exerted on fluid flow is low when the ball valve is in a fully open state. However, the mating surfaces of the valve element and the valve seat must be finished in precision spherical surfaces, elastic members need to be put on the sealing surfaces to secure satisfactory sealing contact, which entails problems similar to those entailed by butterfly valves.
(D) Globe valves are less subject to problems in material and machining than butterfly valves, gate valves and ball valves, and are capable of securing satisfactory sealing contact. However, head loss across globe valves due to resistance exerted on fluid flow is large when the globe valves are in a fully open state.
The problems explained in (A) to (D) by way of example are more serious in large valves and in valves to be used in high-pressure fluid transport lines. Accordingly, it has been believed that it is difficult, from the viewpoint of structure, to achieve the reduction of head loss when the valve is fully open, the reduction of valve element drive torque, the avoidance of abrasion of sealing surfaces due to the sliding movement of the valve element in being seated on the valve seat and the uniform, close contact between the sealing surfaces simultaneously, and any effective techniques to achieve those requirements have not been developed.
Accordingly, it is an object of the present invention to provide a high-performance, economical valve having a simple, rational structure, capable of radically solving those technical problems which could not have been solved, of being easily designed and manufactured, of enabling the use of all kinds of materials including metals and ceramic materials and of enduring the harmful actions of high-temperature, high-pressure slurry and corrosive fluids, and not causing problems when formed in a large size.